Z-67
by Llywela
Summary: Missing scene from The Zygon Inversion. When the crisis is over, Osgood has a question to ask.


**Title** : Z-67  
 **Show** : Doctor Who  
 **Characters** : Twelfth Doctor, Osgood, Clara Oswald, Harry Sullivan (mentions thereof)  
 **Spoilers** : Missing scene from _The Zygon Inversion_. When the crisis is over, Osgood has a question to ask.  
 **Rating** : PG  
 **Disclaimer** : The Doctor, his TARDIS, his companions and his friends belong to the BBC. I have borrowed them for this story and am making no profit from this.

Z-67

"May I ask a question, Doctor?"

Petronella Osgood regarded the Doctor very seriously as they walked together back to his TARDIS on a day so bright and so sunny it was hard to believe that a catastrophic civil war had been only narrowly averted no more than a few hours earlier.

Too many people had died on this bright sunny day, before restoration of the peace to which she'd dedicated her life. That was why she needed to know.

"I know it isn't in the box…so just what did happen to the Z-67 gas that you stole?"

The question hung in the air.

Osgood glanced sideways at the Doctor's profile: lean, angular face and thick grey hair, his shrewd eyes focused on the path ahead, utterly unreadable. She'd always known, of course, that the twin boxes known as the Osgood boxes were empty. She'd helped to develop the concept herself: a stratagem designed to enforce the peace between humankind and the Zygon settlers concealed in their midst, imperfect but effective, and it worked because the weapons believed to be contained within those boxes were known to be real. There _was_ a nuclear bomb. The Z-67 gas _had_ been developed, capable of turning every Zygon on Earth inside out. Just the threat of them was enough, the boxes themselves empty as a safeguard. Misdirection, in case hostilities ever did escalate to that point – as they had today – to ensure that anyone inclined to make use of those terrible weapons expended all their energies looking in the wrong place.

Osgood knew where the nuclear controls were actually housed. But she didn't know what had become of the gas or its formula, stolen by the Doctor so many years ago. Had he destroyed them utterly, since he so obviously disapproved? Or had he kept them somewhere, just in case? In the TARDIS, perhaps? She'd studied him comprehensively, prided herself on her ability to guess what the Doctor would do in all manner of scenarios, but she didn't know what he'd done about this.

He turned to her and smiled, a dazzling, heartfelt smile. "Oh, Osgood, Osgood, Osgood," he said, a twinkle in his eye. "Now that would be telling."

And Clara Oswald, strolling at his other side, glanced up sharply all at once.

"There is no Z-67," she said, a funny look on her face, as if she'd just figured it out. "There never was, was there, Doctor?"

The Doctor laughed. Osgood blinked, confused.

"No, there was," she protested. That much she knew to be fact, she'd seen the paperwork documenting the research, although the research itself had been stolen along with the gas. "Dr Sullivan developed it while he was stationed at Porton Down, using DNA extracted from the bodies of the Zygons who died during the first invasion – it was all stolen, but…"

But the Doctor was still laughing. "What, Harry Sullivan invented a biological weapon of mass destruction? I can't believe anyone fell for that one."

Osgood stared at him, feeling rather as if someone had just pulled a rug out from under her feet.

"It was a lie? The gas was a lie all along?" Never mind the gas, she felt as if her brain was turning itself inside out trying to trace the permutations involved in the hoax. "But Dr Sullivan filed the paperwork for his research over a period of months – his signature, his handwriting – you couldn't have – so he…but why would he lie about a thing like that?"

"Because I asked him to, of course," said the Doctor, as if it should be obvious. Perhaps it was, in hindsight. "Oh, come on, Osgood, I thought you were a fan. You must know that Harry Sullivan was a friend of mine. A friend with a remarkably lurid imagination, if the description he gave of the fake Z-67 is anything to judge by…" He paused, thought about it for a moment. "It's possible he may have been working through a few post-Zygon issues himself when he drew up the paperwork. I hadn't thought of that before. I did tell him to make it sound good."

"You wanted a deterrent," said Clara with a knowing smile. "Something scary. Something that would make everyone think twice, planted in the past to be found when needed in the present. But you didn't want it to actually exist. You just wanted everyone to believe it existed. So you laid a paper trail."

"Not personally," the Doctor corrected her. "I had my friend lay it for me. Far more convincing that way, don't you think?"

"Fake research, fake gas – fake robbery to hide the fakeness of the research and the gas, turn it into a legend and link it to you – but when?" asked Clara. "When did you do it?"

"Oh, ages ago." The Doctor preened, pleased as punch with himself. "Right at the start of all this, before anyone'd had a chance to go trawling through all the records in search of references to the Zygons. I just nipped out of the room for two minutes, popped back a few decades and had a chat with an old friend, asked him to do me a favour, make sure there was something there for them to find. Harry was ideally positioned."

"Because he was at Porton Down," said Osgood. It all made sense now. Even the misdirection was misdirection.

"Developing antidotes to nerve toxins, yes. Harry Sullivan was no killer – but there's no one left now who'd remember that. Just the paperwork he planted on my behalf, telling a different story. Terrible liar, of course, always was, that did give me pause, but it's easier to sound convincing on paper, where no one can see the red cheeks. And he'd had a close personal encounter with the Zygons himself – that gave the ruse a note of plausibility, don't you think?"

"Yes," Osgood admitted. She'd certainly never questioned the story for even a second.

"All I had to do was come back here and shout about it. Mind you, falsifying official documentation isn't exactly cricket." The Doctor dropped into a clipped English accent, a hint of nostalgia in his smile. "So that worried him a bit. But he loved all that cloak-and-dagger spy stuff. And I promised him faithfully it was in aid of a good cause."

The smile faded. He looked troubled, turned back to Osgood and met her gaze with worried eyes.

"Is it a good cause? I've never done this before – allowing alien invaders to settle on an inhabited world that isn't their own, permanently, irrevocably infiltrating a level 5 civilisation. It's against all the rules. But you believe it was the right thing to do, don't you? You believe it's a good cause?"

Osgood thought about the standoff earlier. Truth or consequences, humankind and Zygonkind teetering right on the brink, fingers poised over the buttons…but then pulling back, choosing to end the madness before it was too late.

A fragile peace restored.

"I believe that peace is always a good cause," she said.

~end~

© J. B., November 2015


End file.
